My wife's car threw this code the other day. I cleared it and it returned, so it's legit.

Is there any layman's way to test which of the three likely components failed? I really don't want to put a new cat on it or blow $200 on oxygen sensors when $100 will do. I don't have access to any specialized testing equipment, so I'll be winging it otherwise if there's no easy way to tell.

 

Steelerfan58 I have this same code in my car, my car runs perfect, i replaced both o2 sensors, the catalyic converter on it already is an aftermarket, i checked it, its not melted together inside that i saw, still looked like a honey comb, i dont have emissions where i live so im not even worried about it

 

There is no way to check with out a scan tool or meter....

 

In my experience, 99 times out of 100 a P0420 code is the CAT.

Get an infrared thermometer (you can get them pretty cheap now)

Measure the temp at the front and the back of the CAT. The temp at the back of the CAT should be about 150 degrees hotter than the front. If it's cooler than the inlet, the CAT is shot.

 

Lucky you. I do have to worry about emissions, and the car will not pass with a CEL.

That's actually a big help. I can get my hands on one of those. Thanks very much.

 

It is no help at all because the test is invalid and will not yield a useful answer...

 

Well if there is a change that would be an indication that the catalyst is doing some combustion. Best would be if one could monitor the heat ~700°F for proper operating temp. And monitor the Secondary O2S for voltage. If the primary is normally switching, and the secondary is matching then the catalyst may be degraded. Secondary O2 should show a constant voltage. But if the car is out of tune then the catalyst can only do so much, especially an older catalyst.

 

I've heard this many times and it sounds really reasonable. You can get an infra red thermometer from Harbor Freight and 'though they will probably charge you a restocking fee when you take it back it will be well worth it.

 

He has no "special tools" for monitoring O2 sensor activity.



Proper operating temp is around 1200F-1500F degrees.


What if there is no change between inlet and outlet? Does that mean the cat is bad?

 

UPDATE: The weirdest thing happened last night. My wife is now reporting that the CEL went out all on its own.

I'm at a loss to figure out why the problem "resolved" itself (I'm not entirely sure that it has as yet), but there are two things that come to mind. They may not be related at all, but here they are:

1) She just got her oil changed after running it nearly dry.
2) She recently ran out of gas and I had to bring some to her.

As you might imagine from those (and my first post here), my wife is terrible with cars. But that's where we currently stand. I will continue to monitor and update you further if it returns.

 

On Honda vehicles that are OBD2, when the catalyst falls below 99% efficiency, the MIL will light. Honda is quite proud of its "clean" fleet of vehicles and has the strictest cat monitor in the industry.(Its cat monitor algorithm is much more complex than simply comparing front and rear O2 sensors, as some mistakenly believe.) As a result,once your cat reaches the threshold, it will light the MIL sporadically until complete failure is achieved. Take it to get smogged when the light is off,it will easily pass the sniffer.....

 

A simple obd2 scan tool will do the trick.

Assuming there is no change in temperature that would mean that the cat isn't doing any work. This would mean it's bad.

 

I know ,however he asked for a "laymans" way of testing the fault and said he had no "specialized" tools.....

You would be incorrect. The test is flawed for various reasons and is not valid. There is not one FSM from ANY manufacturer that has a troubleshooting tree for a P0420 or P0430 that involves testing the temp of the cat, and with good reason. It is impossibly to test a cat this way because of the numerous variables involved( Manufacturer,CAT type, CAT monitor state, O2 monitor state, EWMA, etc.....) Save yourself the trouble and forget all about this "test".....

 

You state it's flawed and don't give a reason why. You then proceed to state that manufacturers don't suggest to use this test and again proceed not to give a reason why.

Just because someone doesn't do something doesn't mean it's not correct for someone that does.

 

LoL. I did give a reason,but ok, its obvious you know better than I do.



Moving on....